The present invention relates to a battery pack in which a positive electrode of a battery cell is connected to a negative electrode of another battery cell by a connecting metallic plate, and to a method for welding together the connecting metallic plate and each of the positive and negative electrodes.
A battery pack (also called battery modules) used in hybrid and electric vehicles and mobile devices require charging and discharging large currents and therefore dozens of battery cells connected in series. If the connection resistance (electric resistance) between them is large, conduction loss due to voltage drop increases and heat generation also increases, leading to degradation of characteristics and reduction of the life of the battery pack. Therefore, a number of methods have been proposed for reducing the connection resistance in the battery pack and for coupling battery electrodes of the battery cells.
JP-A-08-287898 proposes a cylindrical battery and a battery pack in which collecting terminals made of a conductive material having surfaces on which a female threaded screw hole or a male screw is provided are connected and fixed to positive and negative electrodes of battery cells through feet that support the surfaces.
JP-A-2004-164981 proposes a battery pack in which a plate made of an electrically insulating resin having a size smaller than the outer circumference of the battery pack is disposed on a positive cap of two battery cells, a projection having a polygonal recess is provided in a valley-like space between battery cells, and a metallic bus-bar that mechanically and electrically interconnects the battery cells is provided on the plate.
JP-A-2000-133227 proposes that metallic lead plates that project outside first and second battery cells are fixed on opposed electrode terminals of battery cells arranged in series and the surfaces of the metallic lead plates are brought into contact with each other.
JP-A-2001-266843 proposes a battery pack in which one of two types of projections of a connecting member is welded onto a sealing element of a battery cell and the other projection is welded onto the bottom surface of an exterior case of the other battery cell.
JP-A-2004-259584 proposes an enclosed battery, a method for manufacturing the enclosed battery, and a cover plate for the enclosed battery in which the backside of a cover plate that seals an opening of a battery case is formed in such a manner that a portion near a filling aperture is formed thinner than the periphery and the filling aperture is sealed by fusion between the thinner portion and a sealing plug.
JP-B2-61-8539 proposes a method for manufacturing a battery including a spiral electrode in which collecting elements, which are a substantially disc-like metallic plane plates, are provided on projecting ends of upper and lower electrodes of a spiral electrode element and the collecting elements are welded to the projecting ends of the electrodes, which intersect with and contact the collecting elements at right angles, by arc spot welding and then these are enclosed in a battery case.